558
FXUS02 KWBC 080647
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
147 AM EST THU DEC 08 2022
VALID 12Z SUN DEC 11 2022 - 12Z THU DEC 15 2022
...HEAVY COASTAL RAINS AND WIDESPREAD MOUNTAIN/INLAND HEAVY
SNOW/WIND THREAT ACROSS THE WEST/ROCKIES INTO SUNDAY/MONDAY...
...DEEP STORM GENESIS/BLIZZARD THREAT WITH HEAVY SNOW AND
TRANSITION AREAS OF ICE/FREEZING RAIN FOR THE NORTH-CENTRAL U.S.
MONDAY PAST MIDWEEK...
...EXCESSIVE RAINFALL AND SEVERE WEATHER THREAT TO SPREAD EASTWARD
FROM THE SOUTH-CENTRAL U.S. MONDAY PAST MIDWEEK...
..OVERVIEW
RAIN SHOWERS AND THUNDERSTORMS ARE POSSIBLE ACROSS THE
SOUTHEASTERN U.S. WITH A WAVY FRONT IN THE VICINITY THIS WEEKEND,
WHILE FARTHER NORTH A POTENT CLIPPER SYSTEM WILL SPREAD RAIN/SNOW
FROM THE GREAT LAKES REGION INTO THE NORTHERN MID-ATLANTIC AND
NORTHEAST BEFORE TRACKING OFFSHORE TO DEVELOP A DEEP ATLANTIC
STORM THREAT OFF THE NORTHEAST TOWARD THE CANADIAN MARITIMES NEXT
WEEK.
HOWEVER, THE MAIN STORY DURING THE MEDIUM RANGE PERIOD WILL BE
UPSTREAM WHERE WELL CLUSTERED GUIDANCE HAVE NOW LOCKED IN ON
DEPICTION OF AN AMPLIFIED TROUGH TO WORK INLAND FROM THE WEST
COAST THROUGH THE WEEKEND, WITH THE DEEPEST REINFORCING ENERGY
ARRIVING SUNDAY INTO MONDAY LEADING TO CLOSED LOW/TROUGH FORMATION
OVER THE INTERMOUNTAIN WEST. THE DYNAMIC SYSTEM WILL LIFT
VIGOROUSLY OVER THE CENTRAL U.S. TUESDAY-THURSDAY. THIS PATTERN
WOULD SUPPORT A PERIOD OF WIDESPREAD AND SIGNIFICANT
TERRAIN-ENHANCED RAIN AND MOUNTAIN SNOW OVER THE WEST THROUGH THE
WEEKEND INTO EARLY NEXT WEEK. THIS IS INCREASINGLY EXPECTED TO BE
FOLLOWED BY EXPANDING/INTENSIFYING RAINFALL OVER THE MISSISSIPPI
VALLEY/VICINITY EASTWARD ACROSS THE EAST-CENTRAL U.S. ALONG WITH
SIGNIFICANT WRAP-BACK SNOW OVER THE NORTH-CENTRAL U.S. EARLY-MID
NEXT WEEK IN ASSOCIATION WITH DEEP STORM/POSSIBLE BLIZZARD GENESIS
AND CORRESPONDING FRONTS. EXPECT MOSTLY BELOW NORMAL HIGH
TEMPERATURES OVER THE WEST AND NEAR TO ABOVE NORMAL PRE-FRONTAL
READINGS OVER MUCH OF THE EASTERN HALF OF THE COUNTRY.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL AND ENSEMBLE FORECASTS HAVE BECOME INCREASINGLY WELL
CLUSTERED WITH RECENT RUNS OVER MEDIUM RANGE TIME SCALES,
BOLSTERING FORECAST CONFIDENCE. A COMPOSITE BLEND OF THE 18 UTC
GFS AND 12 UTC ECMWF/UKMET/CANADIAN SEEMS REASONABLE SUNDAY/MONDAY
AS WELL SUPPORTED BY ENSEMBLES AND THE 01 UTC NATIONAL BLEND OF
MODELS (NBM). PIVOTED TO A BLEND OF BEST CLUSTERED GUIDANCE FROM
THE GFS/ECMWF AND GEFS/ECMWF ENSEMBLES ALONG WITH THE NBM
TUESDAY-THURSDAY THAT SEEMS TO PROVIDE A SOLID FORECAST AMID
GROWING FORECAST SPREAD, BUT STILL WITH ABOVE NORMAL
PREDICTABILITY. THIS SOLUTION MAINTAINS REASONABLE WPC PRODUCT
CONTINUITY AND IS STILL IN LINE WITH NEWEST 00 UTC GUIDANCE.
..WEATHER/HAZARD HIGHLIGHTS
FOR THE WEEKEND, GULF OF MEXICO MOISTURE INFLOW COMBINED WITH A
WAVY SURFACE FRONT AND WEAK UPPER ENERGY MAY SUPPORT MODERATE TO
HEAVY RAINFALL ACROSS THE SOUTHEASTERN PART OF THE COUNTRY.
FARTHER NORTH, PRECIPITATION WILL LIKELY INCLUDE SOME PLOWABLE
SNOW TO SPREAD FROM THE GREAT LAKES THROUGH THE NORTHERN
MID-ATLANTIC AND THE NORTHEAST SUNDAY, WITH HIGHEST WWO
PROBABILITIES NOW OVER THE BEAUTIFUL CATSKILLS.
AS THE MAIN UPPER TROUGH DIGS ACROSS THE WEST THIS WEEKEND AND
SHIFTS EASTWARD THROUGH THE FIRST HALF OF NEXT WEEK, MULTIPLE
HAZARDS ARE LIKELY ACROSS THE COUNTRY. HEAVY PRECIPITATION IS
IMMINENT ACROSS THE WEST THIS WEEKEND/MONDAY, ESPECIALLY INCLUDING
HEAVY TERRAIN-ENHANCED SNOWS ACROSS THE SIERRA NEVADA AND FARTHER
EAST INTO HIGHER ELEVATIONS OF THE GREAT BASIN AND ROCKIES. LOWER
ELEVATION HEAVY RAIN IS ALSO POSSIBLE THIS WEEKEND PARTICULARLY
ACROSS COASTAL AND INTERIOR PARTS OF CALIFORNIA IN CONJUNCTION
WITH A WEAK-MODERATE ATMOSPHERIC RIVER. THEN AS THE UPPER
TROUGH/LOW APPROACHES THE PLAINS AND A SURFACE LOW CONSOLIDATES
AND DEEPENS, AMPLE MOISTURE WILL SPREAD AHEAD OF A COLD FRONT TO
PRODUCE SIGNIFICANT RAINFALL ACROSS THE LOWER/MIDDLE MISSISSIPPI
VALLEY AND VICINITY BEGINNING MONDAY AND ESPECIALLY BY TUESDAY AND
SHIFTING EAST WITH TIME. SOME STRONG TO SEVERE CONVECTION IS ALSO
POSSIBLE, WITH THE STORM PREDICTION CENTER ALREADY MONITORING THIS
POTENTIAL. ON THE BACKSIDE OF THE LOW, COLD TEMPERATURES AND
WRAP-BACK MOISTURE WILL SUPPORT SIGNIFICANT SNOW/WINDS IN THE
NORTHERN PLAINS/UPPER MIDWEST AS SHOWN BY STEADILY INCREASING WPC
WINTER WEATHER OUTLOOK PROBABILITIES AS WELL AS AREAS OF
ICE/FREEZING RAIN IN A TRANSITION ZONE. THIS ALSO SHOWS SOME
WINTRY WEATHER POTENTIAL SPREADING ACROSS THE GREAT LAKES REGION
AND NORTHEAST IN FAVORABLE DOWNSTREAM THETA-E ADVECTION OVER A
PRE-COOLED AIRMASS.
THE WEST SHOULD SEE BELOW NORMAL HIGHS THROUGH THE PERIOD, WITH
THE MOST WIDESPREAD READINGS OF AT LEAST 10-15F BELOW NORMAL AS
THE DEEP UPPER TROUGH CROSSES THE REGION FOR THE FIRST HALF OF
NEXT WEEK. SOME OF THIS COLDER AIR SHOULD SPILL INTO THE HIGH
PLAINS BY NEXT TUESDAY/WEDNESDAY BEHIND THE EXPECTED PLAINS STORM.
ON THE OTHER HAND, SOUTHERN/EASTERN AREAS WILL BE NEAR TO ABOVE
NORMAL FOR TEMPERATURES. ANOMALIES WILL BE GREATEST FOR MORNING
LOWS, WITH SOME PLUS 15-25F ANOMALIES ACROSS THE SOUTHERN TIER
THROUGH MUCH OF THE PERIOD EXPANDING NORTHWARD AT TIMES ACROSS THE
MISSISSIPPI VALLEY. HIGHS ARE FORECAST TO BE AROUND 10-15F ABOVE
NORMAL FOR THE CENTRAL AND THEN EAST-CENTRAL U.S., LOCALLY HIGHER.
SCHICHTEL
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC
MEDIUM RANGE HAZARDS OUTLOOK CHART AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,
QUANTITATIVE PRECIPITATION, EXPERIMENTAL EXCESSIVE RAINFALL
OUTLOOK, WINTER WEATHER OUTLOOK PROBABILITIES AND HEAT INDICES ARE
AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=ERO
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML
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